In August, Pereira, who is responsible for monitoring its isolated groups, led an expedition in the south of the reserve, following reports by an indigenous man of another mass killing.

Mol went with him and took a drone — equipment that FUNAI did not have; the agency has been decimated by budget cuts under the austerity regime of Brazilian President Michel Temer.

As the expedition headed along the Jutai River, around the area where the killing allegedly took place, they came across a small camp on the side of the water that an isolated group had just vacated, leaving an axe, bow, arrows and other artifacts behind.

Then Mol’s drone spotted the main village just a kilometer away, with people, communal thatched buildings and plantations.

They retreated, reasoning that the indigenous group would have moved had they suffered a massacre.

“The drone footage gave us the intel we needed,” Mol said.

Both cases underline just how hard it is to investigate allegations of possible crimes in such remote regions.

In Tabatinga, federal prosecutor Pablo Beltrand said the tip-off of the supposed Jutai River massacre was “not such a reliable report” and presented “contradictions.”

Beltrand has just received FUNAI’s report on the expedition and is analyzing it.

The agency had been reluctant to share sensitive information, such as the location of isolated groups.

That the isolated tribe has stayed in the region is “something to be considered in the investigation,” Beltrand said.

He has yet to conclude his inquiry.

However, he has little to go on — a paddle, a conversation, an anonymous denunciation.

Meanwhile, smaller wooden mining barges are now reportedly being built beside a river in Sao Paulo de Olivenca. The garimpeiros might yet return.